An official website of the United States government
Here's how you know
A .mil website belongs to an official U.S. Department of Defense organization in the United States.
A lock (lock ) or https:// means you’ve safely connected to the .mil website. Share sensitive information only on official, secure websites.


JAN 1947
UDTs become “sea-air” capable for the first time when they begin experimentation with at-sea launch and recovery capabilities from helicopters.

FEB 1948
UDTs begin submersible operations. Lt. Commander Fane and Dr. Chris Lambertsen bring the full spectrum of the OSS-MU diving capabilities to UDTs.

OCT 1948
A UDT detachment from Little Creek conducted operations with the British submersible “Sleeping Beauty.” This was the first time a submersible had been launched and recovered from a U.S. submarine.


The Korean War began on 25 June 1950, when the North Korean Army invaded South Korea. A 10 man UDT detachment is sent from the Pacific UDTs to Japan and dispatched to Korea. The war is primarily land-based, and troops are needed to destroy bridges, trains, roads, and storage facilities. The Underwater Demolition Teams would incorporate all of these new skills into lessons learned and contributed significantly to the evolution of the force.

JUN 1950

The first attempted UDT raid was carried out by Lt. George Atcheson (UDT 3). The team was deployed using inflatable dinghies from the destroyer USS Diachenko (APD0123). The target was to carry out a demolition operation against train transportation by destroying tracks and a tunnel. Soon after landing, the raiders came under heavy North Korean fire and had to abort the mission. Petty Officer 3rd Class Warren “Fins” Foley was wounded and became the first U.S. Navy casualty of the Korean War. This was also the first time that UDTs had operated so far inland.

AUG 1950

OPERATION CHROMITE UDT- 3 support Operation Chromite, the amphibious landing at Inchon. The first combat-diver operation was conducted by UDT member, Chief Gunner’s Mate (GMC) William Giannotti, in October 1950, during mine-clearing operations at Wonsan Harbor. During a dive, Giannotti successfully used an aqualung, self-contained underwater breathing apparatus (SCUBA) to find the sunken USS Pledge and recover classified codes.

SEP - OCT 1950

SEP - OCT 1950

In support of the evacuation of U.S. forces at Hungman Harbor, an eight-man squad set off over 20 tons of explosives. The explosion, set by the UDTs, was the largest single non-nuclear blast since World War II.

DEC 1950

OPERATION FISHNET SEPTEMBER 1952 Operation FISHNET, aimed to reduce North Korea’s food supply by destroying fishnets. This would be the last major operation before the end of the Korean War. 27 JULY 1953 Armistice ends fighting.

SEP 1952

The teams were re-designated. UDTs 1, 3, and 5 became UDTs 11, 12, and 13; and UDTs 2 and 4 became UDTs 21 and 22. Shortly after that, personnel shortages forced the decommissioning of UDT 13, whose men were shared between UDTs 11 and 12. UDT 22 was decommissioned. Odd number prefix is used to designate Pacific Fleet Units and even numbers the Atlantic

FEB 1954

UDTs begin static line parachuting by sending groups of men to U.S. Army jump schools. They go on to innovate water entry methods using tactical and non-tactical diving apparatus.

Chief of Naval Operations, Adm. Arleigh A. Burke, realized the importance of expanding the Navy’s unconvential warfare capabilities and directed OPNAV to organize new or existing Navy units for more minor conflicts. He directed that new units be established possessing the operational experience of the UDTs, but also incorporating the new warfare concepts learned during the Korean War.

JUN 1955 - 1958

May 13, 1961 Adm Wallace H. Beakley, Deputy Chief of Naval Operations, sent a memo to Adm. Burke stating, “I propose that the Navy establish Special Operations Teams as separate components within Underwater Demolition Units One and Two; such forces to be equipped and trained to conduct clandestine missions in support of naval operations. An appropriate cover name for such units could be “SEAL” units, SEAL being a contraction of SEA, AIR, LAND, and thereby, indicating an all-around, universal capability.”

The formation of the SEALs was evolutionary and due to the efforts of numerous individuals. World War II had a similar effect when amphibious warfare drove the development of Underwater Demolition Teams, Scouts and Raiders, Naval Combat Demolition Units, and the Office of Strategic Services Maritime Unit. The global increase of guerrilla warfare and the dangers of conventional and nuclear warfare played important roles in the development of SEALs and other special forces